1. Field of the Invention
The present invention relates to a transparent laminate and a filter using the transparent laminate for use in a plasma display panel (hereinafter referred to as PDP). Particularly, it relates to a PDP filter disposed on the front surface of a PDP which has a basic function of simultaneously cutting electromagnetic waves and near-infrared rays theoretically generated from the PDP and which is superior in visible light transmission characteristic, visible light low reflection characteristic and surface mar-proofness, and a PDP display unit and a PDP front plate provided with the filter stuck thereto.
The present application is based on Japanese Patent Application No. Hei. 11-351094, which is incorporated herein by reference.
2. Description of the Related Art
Transparent laminates each having a metal thin film layer put between transparent dielectric film layers have been discussed with the advance of thin-film-forming technology represented by a vacuum vapor deposition method or a sputtering method. These transparent laminates can utilize both electrically conducting characteristic and infrared reflection characteristic of the metal thin film layer and can provide a function of preventing reflection of visible light on a metal surface by means of the transparent dielectric film layers. For example, these transparent laminates are used in transparent heat-insulating materials for solar cells, green houses for agriculture, window materials for buildings, show-cases for food, and so on, because these transparent laminates transmit visible light rays and reflect heat rays. Further, these laminates are used suitably in electrodes for liquid-crystal displays, electrodes for field light-emitters, electromagnetic wave shielding films, antistatic films, and so on, because these laminates are transparent and exhibit high electrically conducting characteristic. The configurations of these transparent laminates are disclosed, for example, in Japanese Patent Publications No. Sho. 55-11804, Hei. 9-176837, and so on.
On the other hand, with respect to display technology, a plasma display panel (hereinafter referred to as PDP) has been developed as a large-screen display in compliance with the wishes of reduction of thickness and weight and increase of screen size. The PDP generates electric discharge in a gas mainly containing a rare gas, especially neon, enclosed in the panel. Fluorescent substances of R, G and B applied on cells in the panel are made to emit light by vacuum ultraviolet rays generated by the electric discharge. In this light-emitting process, electromagnetic waves and near-infrared rays unnecessary for the operation of the PDP are emitted simultaneously. Particularly, electromagnetic waves not only cause malfunctions of peripheral devices but also have a bad influence on human bodies. Accordingly, it is necessary to cut the electromagnetic waves. Further, the wave length of the near-infrared rays emitted is in a range of from 850 to 1200 nm. On the other hand, the light-receiving sensitivity of remote controllers for domestic electrification products, karaoke, audio and video appliances, and so on, is in a range of from 700 to 1300 nm. There arises a problem that near-infrared rays emitted from the PDP cause the malfunctions of the remote controllers. Accordingly, it is necessary to cut the intensive near-infrared rays theoretically generated from the PDP.
Therefore, a filter capable of simultaneously cutting electromagnetic waves and near-infrared rays generated from the PDP has been discussed. For example, a plate, or the like, formed by sticking or thermally fusion-bonding an acrylic sheet having metal mesh or etching mesh embedded therein to an acrylic sheet mixed with a dye type material for absorbing near-infrared rays has been heretofore used as the filter. Further, as another filter different from such mesh type filter, it has been investigated to apply the aforementioned transparent laminate to a PDP filter.
However, the mesh type filter was easy to obtain a low surface resistance value. The mesh type filter, however, had a problem in image blurring due to a moire phenomenon generated between pixel pitch and electrically conductive mesh, durability of a near-infrared absorbing material, and so on. Further, the amount of the near-infrared absorbing material to be added needed to increase in order to improve the near-infrared cut factor. With the increase of the amount of the near-infrared absorbing material, however, the defects of lowering of the visible light transmission factor and occurrence of color-eye could not be avoided. On the other hand, application of the aforementioned transparent laminate to a PDP filter has been discussed. It is however the existing circumstances that it is impossible to obtain any transparent laminate which can sufficiently satisfy various characteristics such as electromagnetic wave shielding characteristic, near-infrared cutting characteristic, visible light transmission characteristic, low reflection characteristic, low surface resistance, and so on.
In view of the above circumferences, an object of the present invention is to provide a transparent laminate especially suitably used as an optical basic member in a PDP filter, and a light and thin-type PDP filter which satisfies various characteristics such as electromagnetic wave shielding characteristic, near-infrared cutting characteristic, visible light transmission characteristic, visible light low reflection characteristic, low surface resistance, surface mar-proofness, and so on, required by the PDP filter and which is good in visual recognition characteristic. Another object of the present invention is to provide a PDP display unit and a PDP front plate provided with the PDP filter.
As a result of eager discussion in order to solve the above objects, the present inventors have attained the invention which is a transparent laminate comprising: a transparent substrate; a low refractive index transparent thin film formed on a surface of the transparent substrate; n units (3xe2x89xa6nxe2x89xa65) of high refractive index transparent thin films and silver type transparent electrical conductor thin films each unit consisting of high refractive index transparent thin films and silver type transparent electrical conductor thin films, the n units being laminated successively on a surface of the low refractive index transparent thin film; another high refractive index transparent thin film formed on a surface of the n units; and another low refractive index transparent thin film formed on a surface of the other high refractive index transparent thin film, wherein each of the low refractive index transparent thin films is an optically transparent thin film having a refractive index nL in a range of from 1.3 to 1.6 and each of the high refractive index transparent thin films is an optically transparent thin film having a refractive index nH in a range of from 1.9 to 2.5.
In the above optical condition, it is preferable to satisfy the condition that the thickness of the low refractive index transparent thin film formed on a surface of the transparent substrate is 1xc3x97(xcex/4nL), the thickness of the low refractive index transparent thin film in the outermost layer is 2xc3x97(xcex/4nL), the thickness of each of the high refractive index transparent thin films adjacent to the low refractive index transparent thin films is (xc2xd)xc3x97(xcex/4nH), the thickness of each of the high refractive index films sandwiched between the silver type transparent electrical conductor thin films is 1xc3x97(xcex/4nH) and the thickness of each of the silver type transparent electrical conductor thin films is (⅕)xc3x97(xcex/4nH)xc3x97(nHxe2x88x921) when the optical center wavelength xcex is 550 nm. In this condition, the thickness change of each of the low refractive index transparent thin films, the high refractive index transparent thin films and the silver type transparent electrical conductor thin films may be in a range of xc2x120%. Further, instead of forming the low refractive index transparent thin film in the outermost layer, an anti-reflection film, an anti-mirroring film or a low reflection anti-mirroring film is stuck through a transparent self-adhesive agent layer onto a surface of the high refractive index transparent thin film farthest from the transparent substrate.
In this invention, it is preferable that the high refractive index transparent thin film is a thin film made from one compound or two or more compounds selected from the group consisting of indium oxide, tin oxide, titanium dioxide, cerium oxide, zirconium oxide, zinc oxide, tantalum oxide, niobium pentoxide, and zinc sulfide. Further, it is preferable that the silver type transparent electrical conductor thin film is a thin film made from 90% or higher by weight of silver and one compound or two or more elements selected from the group consisting of gold, copper, palladium, platinum, manganese, and cadmium.
Further, the transparent laminate according to the present invention has been obtained by the examination on the factors such as the thickness, the number of configuration layers, the material, the refractive index, the forming manner, and so on, of each of the transparent thin film and the silver type transparent electrical conductor thin film; and by suitable design. It is therefore preferable that the transparent laminate has a visible light transmission factor of not lower than 50%, a visible light reflection factor of not higher than 5%, a surface resistance of not larger than 3xcexa9/xe2x96xa1 and a near-infrared cut factor of not lower than 80% in a region of wave length longer than 800 nm. Further, it is preferable that the transparent laminate is provided with an anti-contamination layer having a thickness of not larger than 10 nm and formed on a surface of the low refractive index transparent thin film in the outermost layer.
Another mode of the present invention relates to a PDP filter using such a transparent laminate, and it is preferable that a transparent pressure sensitive adhesive layer having a thickness in a range of from 10 to 500 xcexcm is formed on a rear surface of the transparent laminate. Owing to the formation of the above-mentioned transparent pressure sensitive adhesive layer, it is possible to provide a PDP display unit wherein a PDP filter is bonded directly to a front display glass portion of a PDP through a transparent pressure sensitive adhesive layer. Further, it is possible to provide a PDP front plate, wherein the front plate is provided with a PDP filter, and a transparent molded body disposed through an air layer on the front side of the PDP, the PDP filter being bonded through a transparent pressure sensitive adhesive layer to a surface of the transparent molded body opposite to the PDP side. In this case, an anti-glare layer or an anti-Newton-ring layer may be formed directly on the PDP side of the transparent molded body disposed through the air layer on the front side of the PDP or is formed on a transparent thin film and bonded through a transparent pressure sensitive adhesive layer to the PDP side of the transparent molded body. Such a PDP front plate is provided on the front surface of a PDP to constitute a PDP display unit.